Thermally conductive silicone grease composition

ABSTRACT

A thermally conductive silicone grease composition comprising:
         (A) an organopolysiloxane having at least two alkenyl groups in one molecule and having a kinetic viscosity of 5,000 to 100,000 mm 2 /s at 25° C.;   (B) a hydrolyzable methylpolysiloxane having a trifunctional termination at one end and represented by the following general formula (2):       

     
       
         
         
             
             
         
       
     
     wherein R 2  represents an alkyl group having 1 to 6 carbon atoms and b is an integer of 5 to 100;
         (C) a thermally conductive filler having a thermal conductivity of at least 10 W/m·° C.;   (D) an organohydrogenpolysiloxane containing from 2 to 5 hydrogen atoms in one molecule directly bound to silicon atoms (Si—H groups);   (E) a bonding aid having a triazine ring and at least one alkenyl group in one molecule; and   (F) a catalyst selected from the group consisting of platinum and platinum compounds.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2010-253762 filed in Japan on Nov. 12, 2010,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a thermally conductive silicone greasecomposition wherein an increase in hardness is lessened and the loweringof elongation is small when thermal aging after curing is carried out athigh temperatures.

BACKGROUND ART

It is widely known that electronic parts such as LSI, IC chips, etc.,generate heat in use and thus, the performance thereof lowers owing tothe heat generation. In order to solve this problem, a variety of heatdissipation techniques have been employed. One of ordinary methodsincludes placing a cooling member in the vicinity of a heat generationunit and bringing them in intimate contact with each other therebydissipating heat by efficient removal of heat through the coolingmember. In this connection, however, if there is a space between theheat generation member and the cooling member, thermal conduction doesnot proceed smoothly because of the presence of air, which is poor inthermal conductivity, so that the temperature of the heat generationmember does not decrease satisfactorily. To prevent this, there havebeen conventionally used, for the purpose of preventing the presence ofair, heat dissipating materials, heat-dissipating sheets or heatdissipating greases, which are good at thermal conductivity and are ableto follow a surface profile of member (Japanese Patent Nos. 2938428,2938429 and 3952184).

Among heat dissipating greases, some greases are imparted with a bondingperformance so as to cause a semiconductor chip and a heat spreader tobe strongly bonded together. However, if there is no grease interventionbetween the semiconductor chip and the heat spreader, a satisfactoryheat dissipation performance is not obtainable to considerably lower theperformance, so that it is important to strongly bond the semiconductorchip and the heat spreader. Although these materials are high in bondingforce, it has been frequently experienced that the hardness of thematerial increases through aging at high temperatures during use. Theelongation of material lowers associated with the increased hardness,with the possibility that the strain of the chip caused by the thermalhistory of heat generation/cooling may not be followed, resulting indetachment or, in the worst case, leading to breakage of the chip.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the above problem.An object of the present invention is to provide a thermally conductivesilicone grease composition, which is smaller in hardness rise and alsoin lowering of elongation than conventional art counterparts whenthermally aged at high temperatures after curing.

We have made intensive studies to achieve the above object and foundthat a thermally conductive silicone grease composition including thefollowing components (A) to (F) is able to provide a cured product thatis small in hardness rise and also in lowering of elongation whenthermally aged at high temperatures.

Therefore, the present invention provides a thermally conductivesilicone grease composition comprising

(A) 100 parts by weight of an organopolysiloxane having at least twoalkenyl groups in one molecule and having a kinetic viscosity of 5,000to 100,000 mm²/s at 25° C.;

(B) 10 to 50 parts by weight of a hydrolyzable methylpolysiloxane havinga trifunctional termination at one end and represented by the followinggeneral formula (2):

wherein R² represents an alkyl group having 1 to 6 carbon atoms and b isan integer of 5 to 100;

(C) 500 to 1,500 parts by weight of a thermally conductive filler havinga thermal conductivity of at least 10 W/m·° C.;

(D) an organohydrogenpolysiloxane containing from 2 to 5 hydrogen atomsdirectly bound to silicon atoms (Si—H groups) in one molecule in such anamount that the number of Si—H groups/the number of the alkenyl groupsof the component (A)=1.7 to 2.8;

(E) 0.05 to 0.5 parts by weight of a bonding aid having a triazine ringand at least one alkenyl group in one molecule; and

(F) a catalyst selected from the group consisting of platinum andplatinum compounds in such an amount of 0.1 to 500 ppm of platinum atomrelative to the component (A).

The composition may further include (G) 0.05 to 0.5 parts by weight, per100 parts by weight of the component (A), of an inhibiting agentselected from the group consisting of an acetylene compound, a nitrogencompound, an organophosphorus compound, an oxime compound and anorganochloro compound.

The thermally conductive silicone grease composition should preferablyhave an elongation at breakage of not smaller than 100% when a sheet ofthe composition after curing at 150° C. for 90 minutes is measuredaccording to a method described in JIS K6251 and an elongation atbreakage of not smaller than 80% after shaping into a 2 mm thick sheetand subsequent aging at 150° C. for 1,000 hours.

ADVANTAGEOUS EFFECT OF INVENTION

The thermally conductive silicone grease composition of the presentinvention is such that hardness rise is small and elongation decrease issuppressed when the composition is heated at high temperatures.

DESCRIPTION OF EMBODIMENTS

The thermally conductive silicone grease composition of the presentinvention includes as essential component:

(A) an alkenyl group-containing organopolysiloxane;(B) a hydrolyzable methylpolysiloxane;(C) a thermally conductive filler;(D) an organohydrogenpolysiloxane;(E) a triazine ring and alkenyl group-containing bonding aid; and(F) a platinum catalyst; and, if required,(G) an addition reaction inhibiting agent.

Component (A)

The organopolysiloxane serving as component (A) included in thecomposition of the present invention has at least two alkenyl groupsdirectly bound to silicon atoms in one molecule and is represented bythe following formula (1)

R¹ _(a)SiO_((4-a)/2)  (1)

wherein R¹ may be the same or different and represents an unsubstitutedor substituted monovalent hydrocarbon group having 1 to 10 carbon atoms,preferably 1 to 8 carbon atoms, and a is a positive number of 1.5 to2.8, preferably 1.8 to 2.5 and more preferably 1.95 to 2.05.

The unsubstituted or substituted monovalent hydrocarbon grouprepresented as R¹ and bound to a silicon atom includes: an alkyl groupsuch as a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, a pentylgroup, a neopentyl group, a hexyl group, a cyclohexyl group, an octylgroup, a nonyl group, a decyl group or the like; an aryl group such as aphenyl group, a tolyl group, a xylyl group, a naphthyl group or thelike; an aralkyl group such as a benzyl group, a phenylethyl group, aphenylpropyl group or the like; an alkenyl group such as a vinyl group,an allyl group, a propenyl group, an isopropenyl group, a butenyl group,a hexenyl group, a cyclohexenyl group, an octenyl group or the like; andthose groups wherein the hydrogen atoms of the groups indicated aboveare partly or wholly substituted with a halogen atom such as fluorine,bromine, chlorine or the like, a cyano group or the like, e.g. achloromethyl group, a chloropropyl group, a bromoethyl group, atrifluoropropyl group, a cyanoethyl group or the like. Preferably, atleast 90 mole % of all the R¹'s is a methyl group.

It is necessary that at least two of all R¹'s be an alkenyl group havingpreferably 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms andmost preferably a vinyl group. The content of the alkenyl groups is at2.0×10⁻⁵ to 1.0×10⁻⁴ mols/g, preferably at 2.0×10⁻⁵ to 6.0×10⁻⁵ mols/g.If the amount of the alkenyl groups is less than 2.0×10⁻⁵ mols/g, theremay be some case where the composition becomes poor in spreadability. Onthe other hand, when the amount exceeds 1.0×10⁻⁴ mols/g, there may bethe case where hardness rise during aging after curing of thecomposition becomes so great that elongation decreases. The alkenylgroups may be bound to a silicon atom at the terminal of the molecularchain or a silicon atom at any position of the molecular chain or boundat both.

The structure of the organopolysiloxane generally has a main chainconsisting of recurring units of diorganosiloxane and is a linearstructure wherein both terminal ends of the molecular chain are blockedwith a triorganosiloxy group, but may partially include a branchedstructure or a cyclic structure.

If the kinetic viscosity of this organopolysiloxane at 25° C. is lowerthan 5,000 mm²/s, hardness rise during thermal aging after curing of thecomposition becomes great, thus decreasing elongation. On the otherhand, when the kinetic viscosity exceeds 100,000 mm²/s, the resultingcomposition becomes poor in spreadability. Hence, the kinetic viscosityis in the range of 5,000 to 100,000 mm²/s, preferably 10,000 to 100,000mm²/s. It will be noted that this kinetic viscosity is a value measuredby means of Ubbelohde-type Ostwald viscometer.

Examples of the component (A) include dimethylpolysiloxanes blocked witha dimethylvinylsilyl group at both ends. These may be used singly or incombination of two or more.

Component (B)

The component (B) used in the present invention is a hydrolyzablemethylpolysiloxane trifunctionally terminated at one end and isrepresented by the following general formula (2)

wherein R² is an alkyl group having 1 to 6 carbon atoms and b is aninteger of 5 to 100.

R² is an alkyl group having 1 to 6 carbon atoms, which includes a methylgroup, an ethyl group, a propyl group, an isopropyl group, a butylgroup, a sec-butyl group, a tert-butyl group, a pentyl group, a hexylgroup or the like. If b in the hydrolyzable methylpolysiloxanetrifunctionally terminated at one end as the component (B) representedby the general formula (2) is smaller than 5, oil breeding from theresulting silicone grease composition becomes considerable, disenablinga bonding performance to be shown. If b is over 100, wettabilityassociated with filler becomes unsatisfactory. For the reasons mentionedabove, b is an integer of 5 to 100, preferably 10 to 60.

The amount of the hydrolyzable methylpolysiloxane trifunctionallyterminated at one end is within a range of 10 to 50 parts by weight per100 parts by weight of the component (A). This is because if the amountis less than 10 parts by weight, satisfactory wettability is not shownand if the amount is greater than 50 parts by weight, bleeding from thecomposition becomes pronounced.

Component (C)

As to the thermally conductive filler of the component (C) having agiven thermal conductivity, if the thermal conductivity is less than 10W/m·° C., thermal conductivity per se of the resulting silicone greasecomposition becomes smaller accordingly. In this sense, the thermalconductivity of filler should be at least 10 W/m·° C. and is preferablyin the range of 10 to 5,000 W/m·° C. As such a thermally conductivefiller, powders of inorganic compounds are usable. The inorganiccompound powders used as the component (C) include one or two or more ofaluminum powder, zinc oxide powder, titanium oxide powder, magnesiumoxide powder, alumina powder, aluminum hydroxide powder, boron nitridepowder, aluminum nitride powder, diamond powder, gold powder, silverpowder, copper powder, carbon powder, nickel powder, indium powder,gallium powder, metallic silicon powder and silicon dioxide powder. Theterm “thermal conductivity” used herein means a value measured by use ofa measuring instrument of QTM-500, made by Kyoto ElectronicsManufacturing Co., Ltd.

If the average particle size of an inorganic compound powder used as thecomponent (C) is either smaller than 0.5 μm or larger than 100 μm, theresulting composition cannot be increased as desired with respect to afilling rate thereof. Therefore, the average size is within a range of0.5 to 100 μm, preferably 1 to 50 μm. In the practice of the presentinvention, the average size means a volume average size [MV] on thevolume basis, which can be measured by Microtrack MT330 OEX, made byNikkiso Co., Ltd. The inorganic compound powder used in the presentinvention may be subjected to hydrophobic treatment with anorganosilane, an organosilazane, an organopolysiloxane, anorganofluorine compound or the like. The hydrophobic treatment may becarried out by ordinary known methods including a method wherein aninorganic compound powder and an organosilane or a partial hydrolyzatethereof are mixed in a mixer such as Trimix, Twin Mix, Planetary Mixer(all being the registered trade names of mixers, made by InoueManufacturing Co., Ltd.), Ultra Mixer (the registered trade name of amixer, made by Mizuho Industrial Co., Ltd.), Hivis Disper Mix (theregistered trade name of a mixer, made by Primix Corporation) or thelike. If necessary, the mixture may be heated to 50° C. to 100° C. Formixing, there may be used a solvent such as toluene, xylene, petroleumether, mineral spirit, isoparaffin, isopropyl alcohol, ethanol or thelike. In this case, the solvent should preferably be removed aftermixing by use of a vacuum apparatus. As a diluting solvent, there may beused an organopolysiloxane used as the component (A), which is a liquidcomponent of the present invention. The composition prepared by thismethod is within the scope of the present invention.

If an amount of the thermally conductive filler (inorganic compoundpowder) is less than 500 parts by weight per 100 parts by weight of thecomponent (A), the resulting composition becomes low in thermalconductivity. If the amount exceeds 1,500 parts by weight, workabilityis degraded owing to an increased viscosity of the composition. Thus,the amount is in the range of 500 to 1,500 parts by weight, morepreferably 600 to 1,300 parts by weight.

Component (D)

The organohydrogenpolysiloxane of the component (D) is one represented,for example, by the following average compositional formula (3)

R³ _(c)H_(d)SiO_((4-c-d)/2)  (3)

wherein R³ represents an unsubstituted or substituted monovalenthydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 10 carbonatoms, c is a value of 0.7 to 2.1, preferably 0.8 to 2.05, and d is avalue of 0.001 to 1.0, preferably 0.005 to 1.0 provided that c+d is apositive value of 0.8 to 3.0, preferably 1.0 to 2.5.

The organohydrogenpolysiloxane having hydrogen atoms directly bound tosilicon atoms (Si-G groups) and serving as the component (D) should haveat least two Si—H groups in the molecule so as to allow the compositionto have a network structure formed by crosslinking. When the Si—H groupsexceed five in number, hardness rise during thermal aging becomesexcessive, so that elongation decreases. Accordingly, the number of theSi—H groups is within a range of 2 to 5.

The residual organic group R³ joined to the silicon atom includes: analkyl group such as a methyl group, an ethyl group, a propyl group, abutyl group, a hexyl group, a dodecyl group or the like; an aryl groupsuch as a phenyl group or the like; an aralkyl group such as a2-phenylethyl group, a 2-phenylpropyl group or the like; a substituted,e.g. a halogen-substituted, hydrocarbon group such as a chloromethylgroup, a 3,3,3-trifluoropropyl group or the like; and an epoxyring-containing organic group (or a glycidyl group or glycidyloxygroup-substituted alkyl group) such as a 2-glycidoxyethyl group, a3-glycidoxypropyl group, a 4-glycidoxybutyl group or the like. Theorganohydrogenpolysiloxane having such Si—H groups may be linear,branched or cyclic, or may be a mixture thereof.

When the amount of the component (D) is such that a ratio of the numberof Si—H groups in the component (D) to the number of the alkenyl groupsin the component (A), i.e. {the number of Si—H groups}/{the number ofalkenyl groups in the component (A)}, is smaller than 1.7, satisfactorybonding performance cannot be shown, thereby worsening adhesion tosubstrate. If the ratio exceeds 2.8, hardness rise during thermal agingbecomes too high, thereby lowering elongation. The ratio is within arange of 1.7 to 2.8, preferably 2.0 to 2.5.

Component (E)

The bonding aid of the component (E) is one that has a triazine ring andat least one alkenyl group in one molecule and is capable of impartingbonding properties to the composition. The alkenyl group contained inthe component (E) may be linear or branched and includes a vinyl group,an allyl group, a 1-butenyl group, a 1-hexenyl group, a 2-methylpropenylgroup, a (meth)acrylic group or the like. In view of costs, an acrylicgroup is preferred. Specific examples of the component (E) are triallylisocyanurate, trimethacryl isocyanurate, and siloxane modified products(derivatives) such as alkoxysilyl-substituted triallyl isocyanurateswherein one to two alkoxysillyl groups, such as a trimethoxysilyl group,are added to one to two allyl groups of the triallyl isocyanurate andhydrolysis condensates thereof.

The component (E) is used within a range of 0.05 to 0.5 parts by weight,preferably 0.05 to 0.3 parts by weight, per 100 parts by weight of thecomponent (A). This is because if the amount is less than 0.05 parts byweight, the resulting composition does not show a satisfactory bondingperformance and if the amount exceeds 0.5 parts by weight,hydrosilylation reaction does not proceed well and thus, no bondingperformance cannot be developed.

Component (F)

The catalyst of the component (F) selected from platinum and platinumcompounds is a promoting component of the addition reaction between thealkenyl group of the component (A) and the Si—H group of the component(D). This component (F) includes, for example, platinum itself,chloroplatinic acid, a platinum-olefin complex, a platinum-alcoholcomplex, a platinum coordination compound or the like. The amount of thecomponent (F) is within a range of 0.1 to 500 ppm relative to the weightof the component (A) because if it is less than 0.1 ppm of platinumatom, no catalytic effect is expected and if it exceeds 500 ppm ofplatinum atom, the effect does not increase, resulting in poor economy.

Component (G)

The inhibiting agent of component (G) is one, which suppresseshydrosilylation reaction at room temperature from proceeding therebyensuring a prolonged shelf life and pot life. As a reaction inhibitingagent, known ones may be used and include acetylene compounds, a varietyof nitrogen compounds, organophosphorus compounds, oxime compounds,organochloro compounds and the like. As to the amount of the component(G), if the amount is smaller than 0.05 parts by weight, an adequateshelf life and pot life cannot be obtained, and if the amount is greaterthan 0.5 parts by weight, curability lowers. Hence, the amount ispreferably within a range of 0.05 to 0.5 parts by weight per 100 partsby weight of the component (A). These may be used after dilution withtoluene or the like in order to allow good dispersion in the siliconegrease composition.

Other Components

Aside from the components (A) to (G) set out above, there may be addedan antioxidant and the like, if necessary, to prevent degradation.

Preparation Method

For the preparation of the thermally conductive silicone greasecomposition of the present invention, there can be adopted a mixingmethod wherein the components (A) to (F) and, if necessary, othercomponents are mixed in a mixer such as Trimix, Twin Mix, PlanetaryMixer (all being the registered trade names of mixers, made by InoueManufacturing Co., Ltd.), Ultra Mixer (the registered trade name of amixer, made by Mizuho Industrial Co., Ltd.), Hivis Disper Mix (theregistered trade name of a mixer, made by Primix Corporation) or thelike.

If viscosity is high, workability becomes worsened. In this sense, thethermally conductive silicone grease composition of the presentinvention should preferably have a viscosity of 10 to 1,000 Pa·s, morepreferably 50 to 1,000 Pa·s. It will be noted that such a viscosity canbe achieved by controlling the components of the silicone greasecomposition as set out above. In the practice of the present invention,the viscosity is measured at 25° C. by means of Malcom viscometer (usingRotor A under conditions of 10 rpm and a shear rate of 6 [l/s]).

The thermally conductive silicone grease composition of the inventioncan be conveniently used by permitting it to intervene betweenelectronic parts such as LSI or other heat-generating members andcooling members thereby dissipating heat through thermal conduction ofheat from the heat-generating member to the cooling member. Thecomposition can be used similarly to existing thermally conductivesilicone grease compositions.

From the standpoint of the strain followability of chip, the siliconegrease composition of the invention should preferably have an elongationat breakage of at least 100%, more preferably at least 120%, when asheet of the composition obtained after curing at 150° C. for 90 minutesis subjected to measurement according to the method described in JISK6251. The upper limit is not critically limited and is generally at upto 400%, preferably at up to 300%. It will be noted that the elongationat breakage can be achieved by using a component (component (A)) havinga large molecular weight to prepare the composition.

Likewise, from the standpoint of the strain followability of chip aftera reliability test of package, the silicone grease composition of thepresent invention should have an elongation at breakage of at least 80%when determined by forming a 2 mm thick sheet and subjecting the sheet,after aging at 150° C. for 1,000 hours, to the method described in JISK6251. Although the upper limit is not critically limited, it isgenerally at up to 300%, preferably at up to 200%. It will be noted thatsuch an elongation at breakage after the aging can be achieved by usinga component (D) having from two to five crosslinking points to preparethe composition.

EXAMPLES

Examples and Comparative Examples are shown to particularly illustratethe present invention, which should not be construed as limited to thefollowing Examples. Tests on the physical properties related to thepresent invention were carried out in the following ways.

[Viscosity]

The absolute viscosity of grease composition was measured by means ofthe Malcom viscometer (Type PC-1T) at 25° C.

[Thermal Conductivity]

The respective compositions were poured into a 3 cm thick mold andcovered with a kitchen wrap, followed by measurement with a device ofModel QTM-500, made by Kyoto Electronic Manufacturing Co., Ltd.

[Elongation at Breakage]

The respective compositions were thermally vulcanized at 150° C. for 90minutes to provide a 2 mm thick sheet, followed by measurement aftershaping the sheet into No. 2 dumbbell, described in JIS K6251.Separately, a sample cured in the form of a sheet was aged at 150° C.for 1,000 hours and its elongation after the aging was measured by asimilar method.

[Bonding Strength]

The respective compositions were each sandwiched between a 1 mm×1 mmsilicon wafer and a 2.5 mm×2.5 mm silicon wafer and thermally heated at150° C. for 90 minutes while pressing with a 1.8 kgf clip, followed bymeasurement of bonding strength by use of Dage series-4000PXY, made byDage Deutchland GmbH.

The following components used to prepare the compositions of the presentinvention were provided.

Component (A)

-   A-1: Dimethylpolysiloxane blocked with a dimethylvinylsilyl group at    opposite ends and having a kinetic viscosity of 30,000 mm²/s at 25°    C.-   A-2: Dimethylpolysiloxane blocked with a dimethylvinylsilyl group at    opposite ends and having a kinetic viscosity of 100,000 mm²/s at 25°    C.-   A-3: Dimethylpolysiloxane blocked with a dimethylvinylsilyl group at    opposite ends and having a kinetic viscosity of 10,000 mm²/s at 25°    C.-   A-4 (Comparative Example):    -   Dimethylpolysiloxane blocked with a dimethylvinylsilyl group at        opposite ends and having a kinetic viscosity of 500,000 mm²/s at        25° C.-   A-5 (Comparative Example):    -   Dimethylpolysiloxane blocked with a dimethylvinylsilyl group at        opposite ends and having a kinetic viscosity of 3,000 mm²/s at        25° C.

Component (B)

-   B-1:

-   B-2:

Component (C)

Two types of aluminum powders and a zinc oxide powder indicated belowwere mixed at mixing ratios, indicated in the following Table 1, at roomtemperature for 15 minutes by use of a 5 liter planetary mixer (made byInoue Manufacturing Co., Ltd., thereby obtaining C-1.

-   -   Aluminum powder having an average size of 2.0 μm (thermal        conductivity: 237 W/m·° C.)    -   Aluminum powder having an average size of 10.0 μm (thermal        conductivity: 237 W/m·° C.)    -   Zinc oxide powder having an average size of 1.0 μm (thermal        conductivity: 25 W/m·° C.)

TABLE 1 Unit: g Aluminum Aluminum powder powder Zinc oxide powderComponent having an average having an average having an average (C) sizeof 2.0 μm size of 10.0 μm size of 1.0 μm C-1 225 500 240

Component (D)

Organohydrogenpolysiloxanes represented by the following formulas

-   D-1:

-   D-2:

-   D-3:

-   D-4 (Comparative Example):

-   D-5 (Comparative Example):

Component (E)

-   E-1:

Component (F)

-   F-1: A-1 solution of a platinum-divinyltetramethyldisiloxane complex    containing 1 wt % of platinum atom

Component (G)

-   G-1: Toluene solution of 50 wt % of 1-ethynyl-1-cyclohexanol

Examples 1 to 7 Comparative Examples 1 to 7

The compositions of Examples 1 to 7 and Comparative Examples 1 to 7 wereobtained by mixing the components (A) to (G) in the following way.

More particularly, component (A) was placed in a 5 liter planetary mixer(made by Inoue Manufacturing Co., Ltd.), to which components (B) and (C)were added in such amounts as indicated in Tables 2 and 3, followed bymixing at 150° C. for one hour. The resulting mixtures were each cooleddown to a normal temperature, to which components (D), (E), (F) and (G)were added in amounts indicated in Tables 2 and 3 and mixed touniformity.

TABLE 2 Formulation Example (parts by weight) 1 2 3 4 5 6 7 Component(A) A-1 100 100 100 100 100 A-2 100 A-3 100 A-4 A-5 Component (B) B-1 5050 40 50 50 50 B-2 50 Component (C) C-1 965 965 850 965 965 965 965Component (D) D-1 1.9 5.5 5.0 D-2 0.66 0.55 0.42 0.8 0.7 D-3 2.3 1.911.47 2.8 2.3 2.1 D-4 D-5 Si—H/Si—Vi 2.4 2.0 2.2 2.0 2.1 2.2 2.0 (numberratio) Component (E) E-1 0.13 0.13 0.13 0.13 0.13 0.13 0.05 Component(F) F-1 0.09 0.09 0.09 0.09 0.09 0.09 0.09 Component (G) G-1 0.13 0.130.13 0.13 0.13 0.13 0.13 Results of evaluation Viscosity (Pa · s) 252261 353 282 248 211 245 Thermal conductivity 2.5 2.5 2.3 2.8 2.5 2.4 2.5(W/m · ° C.) Elongation (%) 133 177 189 131 142 155 138 Elongation afteraging 92 133 139 94 89 109 103 at 150° C. for 1,000 hours (%) Bondingstrength (N) 106 55 58 72 91 43 29

TABLE 3 Formulation Comparative Example (parts by weight) 1 2 3 4 5 6 7Component (A) A-1 100 100 100 100 100 A-2 A-3 A-4 100 A-5 100 Component(B) B-1 50 50 40 50 50 50 B-2 50 Component (C) C-1 965 965 600 965 965965 965 Component (D) D-1 13.2 D-2 0.8 0.44 0.42 0.6 D-3 2.8 1.53 1.475.4 2.1 D-4 1.6 D-5 6.6 Si—H/Si—Vi 2.9 1.6 2.2 2.2 2.2 2.2 2.2 (numberratio) Component (E) E-1 0.13 0.13 0.13 0.13 0.13 0.13 0.6 Component (F)F-1 0.09 0.09 0.09 0.09 0.09 0.09 0.09 Component (G) G-1 0.13 0.13 0.130.13 0.13 0.13 0.13 Results of evaluation Viscosity (Pa · s) 242 252 Not211 284 233 241 Thermal conductivity 2.5 2.5 formed 2.4 2.5 2.4 2.5 (W/m· ° C.) as Elongation (%) 122 202 grease 134 116 Not Not Elongationafter aging 61 162 48 32 formed formed at 150° C. for 1,000 hours (%) asas Bonding strength (N) 31 5 22 114 sheet sheet

As will be seen from the foregoing, the present invention provides athermally conductive silicone grease composition for heat dissipation,which achieves a good balance between the bonding performance and theflexibility of material after high temperature aging. With prior-artcounterparts, if adhesion performance is imparted, a problem is involvedin reliability at the time of high-temperature aging. If reliability isthe first priority, there arises a problem in that bonding performancecannot be imparted. That is, a difficulty has been encountered inbalancing the bonding performance and the reliability at the time ofhigh-temperature aging.

Japanese Patent Application No. 2010-253762 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A thermally conductive silicone grease composition comprising: (A)100 parts by weight of an organopolysiloxane having at least two alkenylgroups in one molecule and having a kinetic viscosity of 5,000 to100,000 mm²/s at 25° C.; (B) 10 to 50 parts by weight of a hydrolyzablemethylpolysiloxane having a trifunctional termination at one end andrepresented by the following general formula (2):

wherein R² represents an alkyl group having 1 to 6 carbon atoms and b isan integer of 5 to 100; (C) 500 to 1,500 parts by weight of a thermallyconductive filler having a thermal conductivity of at least 10 W/m·° C.;(D) an organohydrogenpolysiloxane containing from 2 to 5 hydrogen atomsdirectly bound to silicon atoms (Si—H groups) in such an amount that thenumber of Si—H groups/the number of the alkenyl groups of the component(A)=1.7 to 2.8; (E) 0.05 to 0.5 parts by weight of a bonding aid havinga triazine ring and at least one alkenyl group in one molecule; and (F)a catalyst selected from the group consisting of platinum and platinumcompounds in such an amount of 0.1 to 500 ppm of a platinum atomrelative to the component (A).
 2. The composition according to claim 1,further comprising 0.05 to 0.5 parts by weight, per 100 parts by weightof the component (A), of (G) an inhibiting agent selected from the groupconsisting of an acetylene compound, a nitrogen compound, anorganophosphorus compound, an oxime compound and an organochlorocompound.
 3. The composition according to claim 1 or 2, wherein when asheet obtained by curing said composition at 150° C. for 90 minutes ismeasured according to a method described in JIS K6251, an elongation atbreakage is at least 100% and when said composition is shaped into a 2mm thick sheet and aged at 150° C. for 1,000 hours, an elongation atbreakage is at least 80%.